When two young stars get together, it is never clear how their relationship will play out. Should the pair fail to get along, anyone caught in their path is at risk from violent fallout. But if they are able to settle into a decent rhythm, the stars can grow old together in harmony – and maybe even foster new life.

In fact, computer models suggest that pairs of stars that orbit each other, known as binaries, can be even more hospitable to life than solo stars like our sun, if their relationship helps them to mature quickly. This bodes well for the chances of life elsewhere in the galaxy, because binaries are more common than lone stars.

Spin cycle

Young stars start out with volatile temperaments, which is bad news for nearby planets. The stars' fast rotation rates boost their magnetic field strength, causing them to spit out X-rays and extreme ultraviolet light, along with winds full of high-energy particles. These are harmful to life by themselves, and they can strip vital water from nearby planets' atmospheres.

Stars naturally slow their rotation as they age, reducing their activity and becoming more hospitable. But Paul Mason of the University of Texas at El Paso and colleagues say that some binaries can slow down even earlier in life if their gravitational tango allows them to synchronise their rotation rates.

This extra effect, which the team call rotational ageing, matures binary stars beyond their years, allowing any young planets to retain their water and atmospheres. The team applied their idea to models of the six known binary systems with orbiting planets, which were all discovered by the Kepler spacecraft.

"Some binaries have better habitability factors than in the solar system, while others have worse," says Mason.

Millions more

Of the known systems, Kepler-47 and Kepler-64 appear to be tidally synchronised, providing welcoming environments for planets. Best of all, the Kepler-34 system has a synched pair of sun-like stars, and it might host multiple life-friendly worlds. Systems like Kepler-34 have a much wider habitable zone than our solar system, potentially containing life-friendly twins of Venus and Earth along with further out water worlds totally covered in habitable oceans.

"While this suggests that binary stars may host more habitable worlds, what we don't know yet is how easy it is to form Earth-like worlds around binary stars in the first place," says David Armstrong of Warwick University in the UK, who was not involved in the research. Still, the results could mean there are potentially millions more habitable planets than we thought.

There is also a twist in the tale of these stellar lovers: binaries that orbit extremely close to each other, like the Kepler-16 system, won't slow by much when they synchronise. These stars stay forever young, with a ragingly strong magnetic field. Some couples just aren't meant to grow up and settle down, it seems.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.

The entwined binary stars of the Kepler-35 system (Image: Illustration by Lynette Cook)